Preparing optical memory medium by laminating a thermoplastic resin layer on a thermosetting resin sheet

ABSTRACT

A method for preparing an optical memory medium having forming an uneven guide groove on a plastic resin existing directly or through another layer on a heat-resistant sheet, and laminating an optical recording layer on the surface of the resin layer having said uneven guide groove.

This application is a continuation of application Ser. No. 014,785,filed Feb. 13, 1987, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical memory medium and a method forpreparing the same, particularly a grooved optical memory medium such asflexible optical disc, etc. and a method for preparation thereof.

Further, the present invention relates to a thin type disc and a methodfor preparing the same, particularly a thin type high densityinformation recording disc such as flexible video disc, etc., or agrooved optical information recording substrate and a method forpreparation thereof.

2. Related Background Art

Preparation of a thin type optical memory medium of the prior art hasbeen practiced by first molding a substrate of a thermoplastic resinsuch as polymethyl methacrylate, polycarbonate, etc., by injectionmolding or compression molding into the state in which an uneven guidegroove is provided on the surface, and then laminating an opticalrecording layer on the substrate.

On the other hand, a high density information recording disc has beenprepared by molding a thermoplastic resin such as polymethylmethacrylate, polycarbonate, etc., by injection molding or compressionmolding into the state in which an unevenness for signals is provided onthe surface, followed by cooling and solidification.

According to such methods, it has been difficult to make the medium of athin type, and an optical memory medium with a thickness of 1.0 mm orless could be prepared only with substantial difficulty. This has beenprimarily because of the fact that, as shown in FIG. 16, the substratecould be molded with difficulty for such problems as strength, etc.,unless the thickness of the base portion 41 beneath the uneven guidegroove portion 40 is made considerably thicker relative thereto.

SUMMARY OF THE INVENTION

The present invention has been accomplished in v view of the problems asmentioned above, and its object is to provide a flexible optical discwith a thickness of 1.0 mm or less, etc., and a method for preparing thesame more easily than in the prior art.

According to one aspect of the present invention, there is provided anoptical memory medium comprising a heat-resistant sheet, a plastic resinlayer having an uneven guide groove on the heat-resistant sheet, and anoptical recording layer on the plastic resin layer.

According to another aspect of the present invention, there is provideda method for preparing an optical memory medium which comprises formingan uneven guide groove on a plastic resin existing directly or throughanother layer on a heat-resistant sheet, and laminating an opticalrecording layer on the surface of the resin layer having said unevenguide groove.

According to a further aspect of the present invention, there isprovided a method for preparing a thin type disc which comprisesspreading a resin in a plastic state directly or through another layeronto the respective outer surfaces of heat-resistant sheets comprisingtwo sheets superposed on each other and adhering the resin withsolidification onto the heat-resistant sheets while forming by transferan unevenness for signal onto said resin.

According to still another aspect of the present invention, there isprovided a method for preparing a thin type disc which compriseslaminating on the respective outer surfaces of two heat-resistantsheets, directly or through another layer, a resin having a lower heatdeformation temperature than said heat-resistant sheet to form twolaminated sheets, superposing both of said laminated sheets so that theheat-resistant sheet surfaces may contact each other, transferring anunevenness for signal onto the layer surface of said resin bypressurization of the superposed laminated sheets sandwiched between themold cavities having unevenness on the surface under heating, andthereafter cooling and solidifying the resin.

BRIEF DESCRIPTION OF THE DRAWINGS

5 FIG. 1 is a sectional view showing the state in which a resin in aplastic state is fed to one side of a heat-resistant sheet;

FIG. 2 is a sectional view showing the state in which said resin isspread within a mold;

FIG. 3 is a sectional view showing the state in which a resin underplastic state is fed to both surfaces of a heat-resistant sheet;

FIG. 4 is a sectional view of the state in which said resin is spreadwithin a mold;

FIG. 5 is a view illustrating the coating step of optical recordinglayer;

FIG. 6 and FIG. 8 are each sectional view of a sheet having polymethylmethacrylate laminated on a polyimide film;

FIG. 7 and FIG. 9 are each sectional view showing the step oftransferring the signal of unevenness to said laminated sheet;

FIG. 10 is a view illustrating the step of coating polymethylmethacrylate onto a polyimide film;

FIG. 11 is a view illustrating the step of transferring the guide grooveand coating the light-absorbing dye;

FIG. 12 and FIG. 13 are each schematical view showing an example of thepresent method;

FIG. 14 is a sectional view of a sheet having polymethyl methacrylatelaminated on a polyimide film;

FIG. 15 is a sectional view showing the step for transferring the signalof unevenness to said laminated sheet;

FIG. 16 is a sectional view of a substrate molded according to injectionmolding method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the present invention is described in more detail.

The above object of the present invention can be accomplished byspreading a resin in a plastic state directly or through another layeron one surface or both surfaces of a heat-resistant sheet, adhering withsolidification the resin onto the heat-resistant sheet while forming bytransfer an uneven guide groove onto said resin and thereafterlaminating an optical recording layer capable of recording byphotoenergy on the surface having the uneven guide groove.

In the following, a method for preparing a thin type optical memorymedium having an optical recording layer only on one surface of aheat-resistant sheet is described in detail.

First, a stamper having an uneven surface prepared by electroforming onan original plate is placed on one inner surface of a pair of moldcavities. Further, on the inner surface of the other mold cavity orwithin the space through which the mold cavities are confronted witheach other, a heat-resistant sheet is placed so as to be opposed to thestamper with an interval therefrom. Subsequently, while or afterclamping the mold cavities, the resin in a plastic state is spread inthe space portion constituted by the stamper and the heat-resistantsheet surface within said mold cavity to fill wholly the space portionwith the resin. Said resin is transferred with the uneven guide grooveon its surface with the above stamper and at the same time adhered withsolidification onto the heat-resistant sheet. Thus, a substrate isprepared.

In the present invention, as the method for spreading the resin in aplastic state, there may be employed any of the compression moldingmethod in which a softened resin is compressed in mold cavities whileunder clamping, the cast molding method in which a liquid resin ispoured into clamped mold cavities and the injection molding method inwhich a heated thermoplastic resin is injected into mold cavities.

Also, prior to the step of spreading the resin in a plastic state to beadhered to the heat-resistant sheet in the present invention, forfurther improvement of adhesion force thereof, a layer with strongadhesion (adhesion layer) may be previously provided on theheat-resistant sheet. This adhesion layer serves to not only improve theof adhesive force but it also serves as protection for, theheat-resistant sheet.

As the next step, an optical recording layer is laminated according tothe vapor deposition method or various coating methods such as rollcoating, dip coating, etc., on the surface of the substrate where theguide groove exists, namely on the surface of the resin formed byspreading. According to the steps as described above, a thin typeoptical memory medium can be prepared.

For preparation of a thin type optical memory medium having opticalrecording layers on both surfaces according to the present invention, apair of mold cavities having stampers arranged on the respective innersurfaces may be utilized, and its typical method is shown in Example 2as described below. An optical memory medium having optical recordinglayers on both surfaces has specific features such that it is economicalwith greater information capacity per one sheet and also that warping ofthe medium itself becomes smaller owing to the symmetrical shapes of thefront and back.

According to the method of the present invention, since a substrate ismolded with different kinds of materials of the guide groove portion andthe base portion therebeneath and yet a heat-resistant sheet with highstrength previously molded is used as the base portion, molding of thesubstrate can be easily done if the base portion is not relatively madethicker than the guide groove portion. Therefore, according to thepresent method, the optical memory medium as a whole can be made thinner(see Examples 1 to 2).

Also, the present invention which can accomplish the above objectcomprises having the steps of superposing two sheets of substrateshaving guide grooves prepared by spreading a resin under plastic statedirectly or through another layer on one surface of a heat-resistantsheet and adhering with solidification onto the heat-resistant sheetwhile forming by transfer unevenness for signal onto said resin so thatsaid heat-resistant sheet surfaces may contact each other, andlaminating optical recording layers capable of recording by photoenergyon the both external surfaces having the guide grooves.

In this embodiment of the present invention, first a stamper having anuneven surface prepared by electroforming on an original plate is placedon the inner surface of one of a pair of mold cavities. Further, on theinner surface of the other mold cavity or within the space through whichthe mold cavities are opposed to each other, a heat-resistant sheet isplaced with an interval from the stamper and as opposed thereto(step-1). Subsequently, while or after clamping the mold cavity, theresin under plastic state is spread in the space portion constituted bythe stamper and the heat-resistant sheet surface within said moldcavities to fill wholly the space portion with the resin (step-2). Saidresin is transferred with the uneven guide groove on its surface withthe above stamper simultaneously with adhesion to the heat-resistantsheet. Thus, one sheet of substrate is prepared. Such method ispracticed again to prepare two sheets of substrates (step-2'). Also, twosheets of substrates may be formed at the same time according to thefollowing method. That is, stampers are placed on both inner surfaces ofa pair of mold cavities, and a heat-resistant sheet having two sheetssuperposed on one another is arranged within the space through which thecavities are opposed to each other, followed by practicing the stepsimilar to the step-2, whereby two sheets can be prepared at the sametime.

Next, the two sheets of substrates obtained in the above steps aresuperposed on one another so that the heat-resistant sheets may contacteach other (step-3). Both substrates are left to be unadhered. Then, onboth surfaces of the superposed substrates, namely the surfaces whereguide grooves are formed, optical recording layers capable of recordingby photoenergy are laminated (step-4). Thus, two sheets of opticalmemory media are prepared at the same time. The recording layer may beformed by laminating the material as described below according to thevapor deposition method or various coating methods such as dip coating,roll coating, etc.

According to the method of the present invention, as described above,the substrate is molded with different kinds of materials in the guidegroove portion and the base portion therebeneath, allowing aheat-resistant sheet with high strength and previously molded to be usedas the base portion, making the molding of the substrate easily done ifthe base portion is not made relatively thicker than the guide grooveportion. Therefore, according to the present invention, the opticalmemory medium as a whole can be made thinner.

Also, since two sheets of optical recording layer can be formed at thesame time, productivity can be improved. Further, in the present method,since the respective back faces of the two sheets of substrates are notexposed during lamination of the optical recording layer, it is notnecessary at all to cover the back surfaces of the substrate withcoverings, etc., even when utilizing dip coating as the laminationmethod, whereby dip coating can be practiced with extreme ease. (SeeExample 3).

Also, the above object of the present invention can be accomplished bylaminating on one surface or both surfaces of a heat-resistant sheet aresin having a lower heat distortion temperature than saidheat-resistant sheet (hereinafter abbreviated as readily deformableresin) directly or through another layer, transferring an uneven guidegroove on the surface of said resin layer by pressurization of thelaminated sheet obtained between the mold cavities having unevenness onthe surface under heating and thereafter laminating an optical recordinglayer capable of recording by photoenergy on the surface having saidguide groove.

In this embodiment of the present invention, first a readily deformableresin is laminated on one surface or both surfaces of a heat-resistantsheet to form a laminated sheet. As the laminating method, there may beemployed the method in which the readily deformable resin is dissolvedin a solvent, etc., and the solution is coated on a heat-resistant sheetby roll coating and the method in which the readily deformable resin isformed into a film and laminated onto a heat-resistant sheet. Also, thereadily deformable resin may be plastered with the heat-resistant sheetthrough a intermediary adhesion layer. According to this method,sufficiently great adhesion force can be obtained and the heat-resistantsheet can be protected with the adhesion layer. Next, the abovelaminated sheet is pressurized by sandwiching under heat to transfer theuneven guide groove onto the surface of the readily deformable resinlayer to provide a substrate. Pressurization of the laminated sheethaving the readily deformable resin on both surfaces by sandwiching maybe practiced by use of a pair of mold cavities having unevenness on theinner surfaces respectively. Pressurization of a laminated sheet havingthe readily deformable resin layer only on one surface may be practicedby use of a pair of mold cavities having unevenness only on one innersurface thereof.

The means for heating during pressurization by sandwiching may beprovided in the mold itself or prepared separately from the mold.

Subsequently, on the surface of the substrate where the guide groove istransferred, namely on the readily deformable resin layer surface, anoptical recording layer capable of recording by photoenergy is laminatedaccording to various lamination methods such as the vapor depositionmethod, the roll coating method, the dip coating method, etc. Accordingto the steps as described above, a thin type optical memory medium canbe prepared.

An optical memory medium having optical recording layers on bothsurfaces has the advantages such that it is economical with greaterinformation capacity per one sheet and also that warping of the opticalmemory medium itself becomes smaller due to the symmetrical shapes offront and back.

According to the method of the present invention, as described above,since the substrate is molded with different kinds of materials of theguide groove portion and the base portion therebeneath, and yet aheat-resistant sheet with high strength previously molded is used as thebase portion, formation of the substrate can be easily done, if the baseportion is not made relatively thicker than the guide groove portion.

Also, in the present invention, since no step of filling the startingmaterial resin within the mold cavity is required as in injectionmolding, the restriction with respect to the cavity width set in themold cavity is very small, and therefore the substrate can be madethinner also in this respect.

For the above reasons, according to the present method, the opticalmemory medium as a whole can be made thinner (see Examples 4 and 5).

Also, the present invention capable of accomplishing the above objectrelates to a method for preparing a thin type optical memory medium,which comprises having the steps of laminating on one surface of aheat-resistant sheet a resin having a lower heat distortion temperaturethan said heat-resistant sheet directly or through another layer,pressurizing the laminated sheet obtained under heat by sandwichingbetween mold cavities having unevenness on the surface to transfer theuneven guide groove onto the surface of said resin layer, superposingthe two sheets of the laminated sheets thus formed so that theheat-resistant sheet surfaces may contact each other, and laminatingoptical recording layers capable of recording with photoenergy on bothsurfaces having said guide grooves.

In this embodiment of the present invention, first a readily deformableresin is laminated on one surface of a heat-resistant sheet to form alaminated sheet. As the lamination method, there may be employed themethod in which the readily deformable resin is dissolved in a solvent,etc., and a resultant solution is coated onto a heat-resistant sheet byroll coating or the method in which the readily deformable resin isformed into a film and laminated onto the heat-resistant sheet, etc.Also, the readily deformable resin and the heat-resistant sheet may beplastered through an intermediary adhesion layer. According to thismethod, sufficiently great adhesive force can be obtained and also theheat-resistant sheet can be protected with the adhesion layer.

By practicing again the method as described above, two laminated sheetsare formed. As another method for forming two of laminated sheets, theremay be also employed the method in which two heat-resistant sheets aresuperposed on one another and dip coating is effected on both surfacesthereof. This method is preferable in that the two laminated sheets canbe obtained at the same time.

As the next step, on each readily deformable resin surface of the twolaminated sheets, an uneven guide groove is transferred to form twosubstrates. As in the transfer method, there may be employed the methodin which the laminated sheet is pressurized one by one by sandwichingbetween a pair of mold cavities of which only one inner surface isshaped in unevenness or the method in which the two laminated sheets aresuperposed on one another so that the respective heat-resistant sheetsmay contact each other and pressurized under heating by sandwichingbetween a pair of mold cavities of which the respective inner surfaceshave unevenness. According to the latter method, there is the advantageof smaller warping of the substrate because pressurization bysandwiching can be done under the symmetrical state of front and back.

Next, the two substrates are superposed so that the respectiveheat-resistant sheet surfaces may contact each other, and opticalrecording layers capable of recording by photoenergy are laminated onthe both surfaces thereof, namely readily deformable resin layersurfaces provided with the guide grooves, thereby forming two sheets ofoptical memory media at the same time. Lamination of the opticalrecording layer may be practiced by laminating the material as describedbelow according to the vapor deposition method or various coatingmethods such as dip coating, roll coating, etc.

In the method of the present invention, as described above, since thesubstrate is molded with different kinds of materials of the guidegroove portion and the base portion therebeneath and yet aheat-resistant sheet with high strength previously molded is used as thebase portion, molding of the substrate can be easily done if the baseportion is not made relatively thicker than the guide groove portion.

Also, in the present invention, no step of filling the starting materialresin within the mold cavity is required as in injection molding, andtherefore limitation with respect to the cavity width set in the moldcavity can be very small, and the substrate can be made thinner also inthis respect. For the above reasons, according to the present method,the optical memory medium as a whole can be also made thinner.

Also, since two sheets of optical recording layers can be formed at thesame time, productivity can be improved.

Further, in the present method, since the respective back faces of thetwo substrates are not exposed during lamination of optical recordinglayers, it is not necessary at all to cover the back faces of thesubstrate with coverings, etc., even in the case of utilizing dipcoating as the lamination method, whereby dip coating can be practicedwith extreme ease (see Example 6).

Further, the method for preparing a thin type disc of the presentinvention which can accomplish the above object comprises spreading aresin under plastic state directly or through another layer on therespective outer surfaces of a heat-resistant sheet comprising twosheets superposed on one another and adhering the resin withsolidification onto the heat-resistant sheet while forming by transfergrooves of unevenness for embodying signal onto said resin.

In this embodiment of the present invention, first stampers each havingan uneven surface prepared by electroforming on an original plate areplaced on both inner surfaces of a pair of mold cavities. Further,within a space through which a pair of mold cavities are opposed to eachother, two sheets of superposed heat-resistant sheets are placed with aninterval from both stampers and as opposed thereto. The twoheat-resistant sheets are superposed on one another but left to beunadhered.

Next, while or after clamping the mold cavities, in the spaceconstituted by the stampers and the heat-resistant sheet surfaces withinsaid mold cavities, the resin under plastic state is spread to fill thespace with the resin. Said resin is transferred with unevenness forsignal on its surface with the above stampers simultaneously withadhesion by solidification onto the heat-resistant sheets, whereby twosheets of thin type discs can be formed at the same time. In the presentinvention, as the method for spreading the resin under plastic state,there may be employed any of the compression molding method in which asoftened resin is compressed by mold cavities under clamping, the castmolding method in which a liquid resin is poured into clamped moldcavities and the injection molding method in which a heatedthermoplastic resin is injected into mold cavities.

Also, prior to the step of spreading the resin under plastic state to beadhered onto the heat-resistant sheet, for further improvement ofadhesive force thereof, a layer with strong adhesiveness (adhesionlayer) may be also previously provided on the heat-resistant sheet. Thisadhesion layer serves to not only to improve adhesion between layers butalso protects the heat-resistant sheet.

In the method of the present invention, since a thin type disc is moldedwith the use of different kinds of materials of the uneven portion forsignal and the base portion therebeneath, and yet a heat-resistant sheetwith high strength previously molded as the base portion, formation ofthe disc can be easily done if the base portion is not made relativelythicker than the unevenness portion. Thus, the disc can be made thinneraccording to the present method.

Further, the present invention has the following advantages:

(1) since two sheets of thin type discs can be prepared at the sametime, productivity is high; and

(2) since the preparation steps proceed under the state where twoheat-resistant sheets are arranged symmetrically, the strain at thesignal portion formed on said heat-resistant sheet in the intermediatespreading step can be small. (see Example 7).

Also, the above object of the present invention can be accomplished bylaminating on each surface of two heat-resistant sheets a resin having alower heat distortion temperature than said heat-resistant sheet(hereinafter abbreviated as readily deformable resin) directly orthrough another layer to form two laminated sheets, superposing saidboth laminated sheets so that the heat-resistant sheet surfaces maycontact each other, transferring an unevenness for signal onto the layersurface of said resin by pressurization of the superposed laminatedsheets under heating by sandwiching between the mold cavities havingunevenness on the surface, and thereafter cooling and solidifying theresin.

In this embodiment of the present invention, first a readily deformableresin is laminated on one surface of the heat-resistant sheet to form alaminated sheet. As the lamination method, there may be employed themethod, in which the readily deformable resin is dissolved in a solvent,etc., and the resultant solution is coated onto a heat-resistant sheetby roll coating or the method in which the readily deformable resin isformed into a film and laminated onto heat-resistant sheet, etc. Also,the readily deformable resin may be plastered with a heat-resistantsheet through an adhesion layer. According to this method, sufficientlygreat adhesive force can be obtained, and also the heat-resistant sheetscan be protected with the adhesion layer.

By practicing again the method as described above, two laminated sheetsare formed. Subsequently, the two laminated sheets are superposed on oneanother so that the heat-resistant sheets may contact each other. Inthis case, both sheets are not fixed with an adhesive, etc.

As the next step, both surfaces of the superposed laminated sheets,namely the readily deformable resin surfaces are pressurized underheating by sandwiching to transfer the unevenness for signal on bothsurfaces. The pressurization by sandwiching may be practiced by use of apair of mold cavities having unevenness respectively on the innersurfaces. The heating means during pressurization by sandwiching may beprovided in the mold itself, or separately from the mold.

After the above transfer step, via cooling and solidification, twosheets of thin type discs are obtained at the same time.

The above thin type disc can be itself used as high density informationrecording disc, and also an optical disc which can be also used foroptical reproduction system can be obtained by applying post-treatmentsuch as metal vapor deposition, coating of light-absorbing dye, etc. Inthe method of the present invention, as described above, since theuneven portion for signal and the base portion therebeneath are moldedwith different kinds of materials, and yet a heat-resistant sheet withhigh strength previously molded is used as the base portion, molding canbe easily done if the base portion is not made relatively thicker thanthe uneven portion for signal.

Also, in the present invention, no step of filling the starting materialresin in the mold cavity is required as in injection molding, andtherefore limitation with respect to the cavity width set in the moldcavity is extremely small, and the substrate can be made thinner also inthis respect.

For the above reasons, according to this method, the optical memorymedium as a whole can be made thinner.

Further, the present invention has the following advantages:

(1) since two sheets of thin type discs are prepared at the same time,productivity is high;

(1) since two heat-resistant sheets are pressurized by sandwiching underthe state symmetrically arranged, unbalance in force applied on therespective portions is small, whereby the respective discs aftercompletion have little strain. (see Example 8)

The heat-resistant sheet to be used in the present invention, namely thefilm to be used as the base is flexibly capable of standing thetemperature of the resin under plastic state during formation ofunevenness pattern, preferably a thermosetting heat-resistant film.Typical examples of the thermosetting heat-resistant film may includepolyimide film, polyamideimide film, epoxy resin film, silicone resinfilm, poly-esterimide film, polyester film and fluorine resin films suchas tetrafluoroethylene-hexafluoropropylene copolymer film,tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer film, etc.Also, as the heat-resistant sheet, a material which is not flexible suchas a plate can be used.

As the resin to be used in the present invention for forming a guidegroove on the surface, thermoplastic resins are preferred. Typicalexamples of the thermoplastic resin may include polysulfone,polyolefins, polyolefin copolymers such as ethylene-vinyl acetatecopolymer, ethylene-acrylate copolymer, ethylenepropylene copolymer,etc., polyolefin halides, vinyl chloride copolymers such as vinylacetate-vinyl chloride copolymer, vinyl chloride-acrylonitrilecopolymer, etc., vinylidene chloride copolymers such as vinylidenechloride-vinyl chloride copolymer, vinylidene chloridevinylchrolide-acrylonitrile copolymer, etc., polystyrene, styrene copolymerssuch as styreneacrylonitrile copolymer (AS resin),styrene-acrylonitrile-butadiene copolymer (ABS resin), etc.,p-methylstyrol, 2,5-dichlorostyrol, vinylanthracene, etc. or copolymersthereof (styrol copolymers), cumarone and indene or copolymers thereofwith styrene, terpene resin or picolite, acrylic resins,polyacrylonitrile, acrylonitrile copolymers such as acrylonitrile-vinylacetate copolymer, acrylonitrilevinyl pyridine copolymer,acrylonitrile-methyl methacrylate copolymer, etc., polyacrylamide,diacetone acrylamide polymer prepared by reacting acetone withacrylonitrile, polyvinyl acetate, copolymers of vinyl acetate withacrylate ester, vinyl ester, vinyl ether or ethylene, etc., polyvinylether, polyamide, thermoplastic polyesters, polyvinyl alcohols, orpolyvinyl acetal type resins, polyurethane, polyvinylcarbazole with anumber average molecular weight of 6000 or less or polyvinylcarbazolecopolymers of vinylcarbazol and ethylene or styrene, etc., and othernitrogen containing vinyl polymers, polybutadiene, or diene typepolymers such as butadiene-styrene copolymer or isoprene-isobutylenecopolymer, etc., polyether, polycarbonate, polyethyleneimines, cellulosetype resin or blends of two kinds or more of the above resins, or blendswith other thermoplastic resins.

As the material for the optical recording layer to be used in thepresent invention, any kind of materials is useful, provided it can forma thin film cable of recording by light. For example, metals such asaluminum, inorganic compounds such as bismuth, tellurium oxide orchalcogenide type compounds may be employed. These materials can be madeinto optical recording layers generally be sputtering or vacuum vapordeposition. Also, as other optical recording materials, those composedmainly of light-absorbing coloring matter may be employed. Examples oflight-absorbing coloring matter may include azo, stilbene,phthalocyanine type direct dyes including cyanine, melocyanine,triphenylmethane, naphthoquinone, xanthene, squalium and azulene, etc.;acidic dyes such as azo, anthraquinone, triphenylmethane, xanthene andazine type; basic dyes such as cyanine, azo, azine, triphenylmethanetype; mordant acidic mordant dyes such as azo, anthraquinone, xanthene,triphenylmethane type; vat dyes such as anthraquinone, indigoid type;oil soluble dyes such as azo, anthraquinone, phthalocyanine,triphenylmethane type, etc. These can be formed into optical recordinglayers according to various coating methods or the like as mentionedabove.

EXAMPLE 1

In FIG. 1, a stamper 2 having unevenness on the surface prepared byelectroforming on an original plate was placed in one mold cavity 3, anda polyimide tape with a thickness of 50 μm having a thermal softeningtemperature of 300° C. or higher was placed in the other cavity mold 4as the heat-resistant sheet 1. To the center of the stamper 2 was fed apolymethyl methacrylate resin 5 having a number average molecular weightof 80000 softened to be under plastic state, and said resin 5 wascompressed with the mold cavities 3 and 4. Said resin 5 flowed from thecenter of the mold cavity toward the circumferential direction untilspread wholly within the mold cavity as shown in FIG. 2 to be adhered tothe heat-resistant sheet 1 simultaneously with formation of uneven guidegroove on its surface with the stamper 2.

A 1% solution of a light-absorbing dye having the structural formulashown below (solvent ... diacetone alcohol : isopropyl alcohol =2 : 1parts by weight): ##STR1## was applied on the resin having the guidegroove formed thereon according to the roll coating method, followed byevaporation of the solvent to form an optical recording layer. Thus, athin type optical memory medium was obtained.

EXAMPLE 2

In FIG. 3, two stampers 2 having unevenness on the surface prepared byelectroforming on original plates were placed respectively on bothsurfaces of the mold cavities 3, 4 and a polyimide tape with a thicknessof 50 μhaving a thermal softening temperature of 300° C. or higher wasarranged as the heat-resistant sheet 1 between the two stampers. To bothsides near the center of the heat-resistant sheet 1 was fed a softenedpolymethyl methacrylate resin 5 having a number average molecular weightof 80000 and said resin 5 and the heat-resistant sheet 1 were compressedfrom both sides with mold cavities 3 and 4. The resin 5 flowed from thecenter of the mold cavity toward the circumferential direction untilspread wholly within the mold cavities as shown in FIG. 4 to be adheredto the heat-resistant sheet 1, simultaneously with formation of a guidegroove in shape of an uneven pattern on its surface with the stampers 2.On both surfaces of the substrates thus formed, the same light-absorbingcoloring matter solution as in Example 1 was then laminated according todip coating, followed by evaporation of the solvent to obtain an opticalmemory medium.

The thicknesses of the memory media completed in Examples 1 and 2 wereas follows.

    ______________________________________                                                    Thickness (μm)                                                 ______________________________________                                        Example 1      90                                                             2             130                                                             ______________________________________                                    

EXAMPLE 3

In FIG. 1, a stamper 2 having unevenness on the surface prepared byelectroforming on an original plate was placed in one mold cavity 3, anda polyimide tape with a thickness of 50 μm having a thermal softeningtemperature of 300° C. or higher was placed in the other cavity mold 4as the heat-resistant sheet 1. To the center of the stamper 2 was fed asoftened polymethyl methacrylate resin 5 having a number averagemolecular weight of 80000, and said resin 5 was compressed with the moldcavities 3 and 4. Said resin 5 flowed from the center of the mold cavitytoward the circumferential direction until spread wholly within the moldcavity as shown in FIG. 2 to be adhered to the heat-resistant sheet 1simultaneously with formation of uneven guide groove on its surface withthe stamper 2. Two sheets of substrates prepared in the above steps weresuperposed on one another so that one surface of the heat-resistantsheet may be contacted as shown in FIG. 5 and, the laminate obtained wassubjected to dip coating of an optical recording layer on the guidegroove by passing through a 1% solution of the above light-absorbing dye6 (solvent ... diacetone alcohol:isopropyl alcohol =2:1 parts by weight)with the roll 7, and thereafter the two sheets were separated by theseparating roll 8 to obtain two sheets of thin type optical discs at thesame time. Each thin type optical disc had a thickness of 90 μm.

EXAMPLE 4

A polymethyl methacrylate having a heat distortion temperature of 85° C.and a number average molecular weight of 80000 (readily deformableresin) was dissolved in toluene, and the resultant solution was appliedto a uniform thickness according to roll coating on a film (heatresistant sheet) 9 with a thickness of 50 μm and having a heatdistortion temperature of 300° C. or higher (captone film produced byToray K.K.) in FIG. 6. When the polyimide film 9 coated with saidsolution was dried by heating at 100° C. for 1 hour, a polymethylmethacrylate layer 10 with a thickness of 50 μm remained afterevaporation of toluene to give a laminated sheet 11. In FIG. 7, as thepress portion, a stamper 12 having an uneven surface prepared byelectroforming an original plate was mounted in the mold cavity 13, anda cushion layer 14 in the mold cavity 15. After the laminated sheet 11was pressed by heating by the above press portion to transfer the unevenguide groove onto the polymethyl methacrylate layer 10, the resin wascooled and solidified to provide a substrate.

Then, a 1% solution of the above light-absorbing dye (solvent ...diacetone alcohol:isopropyl alcohol =2:1 parts by weight) was applied onthe substrate by roll coating, followed by evaporation of the solvent toform an optical recording layer. Thus, a thin type optical memory mediumwas obtained.

EXAMPLE 5

A polymethyl methacrylate having a heat distortion temperature of 85° C.and a number average molecular weight of 80000 (readily deformableresin) was dissolved in toluene, and the resultant solution was appliedto a uniform thickness by roll coating on both surfaces of a polyimidefilm (heat-resistant sheet) 9 with a thickness of 50 μm having a heatdistortion temperature of 300° C. or higher (captone film produced byToray K.K.) shown in FIG. 8. When the polyimide film 9 coated with saidsolution was dried by heating at 100° C. for 1 hour, polymethylmethacrylate layers 10 with a thickness of 50 μm remained on bothsurfaces of the polyimide film 9 after evaporation of toluene to give alaminated sheet 16. In FIG. 9, as the press portions, stampers 12 havinguneven surfaces prepared by electroforming original plates were mountedrespectively in mold cavities 13 nd 15. After the laminated sheet 16 waspressed by the above press portions to transfer uneven guide groovesonto the polymethyl methacrylate layers 10, the resin was cooled andsolidified to provide a substrate. Then, the same light-absorbingcoloring matter solution as in Example 4 was applied on both surfaces ofthe substrate by dip coating, followed by evaporation of the solvent toform an optical recording layer. Thus, a thin type optical memory mediumwas obtained. The optical memory media prepared in Examples 4 and 5 hadthicknesses shown below.

    ______________________________________                                                    Thickness (mm)                                                    ______________________________________                                        Example 4     0.10                                                            5             0.15                                                            ______________________________________                                    

EXAMPLE 6

As shown in FIG. 10, two sheets of a film 17 with a thickness of 50 μmhaving a heat distortion temperature of 300° C. (captone film producedby Toray K.K.) were contacted with each other by a pressure roll 18 andpassed through a solution 19 containing a polymethyl methacrylate havinga heat distortion temperature of 85° C. and a number average molecularweight of 80000 dissolved in toluene to thereby coat the both surfaces(each one surface of the two sheets of the polyimide film) with thepolymethyl methacrylate. Then, toluene was evaporated in a heatingsurface 20 to laminate a polymethyl methacrylate layer with a thicknessof 50 μm, thus forming two sheets of laminated sheets (FIG. 10).Thereafter, as shown in FIG. 11, guide grooves were transferred onto thepolymethyl methacrylate layers by pressing under heating with the pressportions having stampers 23 and 24 having unevenness on the surfaceprepared by electroforming original plates mounted in the mold cavities21 and 22, respectively, followed by cooling and solidification.

Subsequently, by passing through a 1% solution of the abovelight-absorbing dye 25 (solvent ... diacetone alcohol:isopropyl alcohol=2:1 parts by weight), the light-absorbing dye was coated on the guidegrooves, followed by evaporation of the solvent to form opticalrecording layers. Then, the two sheets were separated by a separatingroll 26 to obtain two sheets of thin type optical memory media. Eachmedium and a thickness of 0.1 mm.

EXAMPLE 7

In FIG. 12, two stampers 27 having unevenness on the surface prepared byapplication of electroforming working on original plates were placed onboth surfaces of the mold cavity 28, and two sheets of a polyimide tapewith a thickness of 50 μm having a thermal decomposition temperature of300° C. or higher were placed superposed on one another as theheat-resistant sheet 29 between the two stampers 27. To both sides nearthe center of the two sheets of heat-resistant sheet 29 was fed asoftened polymethyl methacrylate resin 30 having a number averagemolecular weight of 80000, and said resin 30 and the heat-resistantsheet 29 were compressed by the mold cavity 28. Said resin 30 flowedfrom the center of the mold cavity toward the circumference until spreadwholly within the mold cavity as shown in FIG. 13 to be adhered andsolidified to the two sheets of heat-resistant sheet 29, simultaneouslywith formation of an uneven pattern on their surfaces by the stamper 27.

EXAMPLE 8

A polymethyl methacrylate having a heat distortion temperature of 85° C.and a number average molecular weight of 80000 (readily deformableresin) was dissolved in toluene, and the resultant solution was appliedto a uniform thickness by roll coating on one surface of a film(heat-resistant sheet) 31 with a thickness of 50 μm having aheat-distortion temperature of 300° C. or higher (captone polyimido filmproduced by Toray K.K.) shown in FIG. 14. When the polyimide film 31coated with said solution was dried by heating at 100° C. for 1 hour, apolymethyl methacrylate layer 32 with a thickness of 50 μm remained onone surface of the polyimide film after evaporation of toluene to give alaminated sheet 33. The above steps were practiced again to form anothersheet of laminated sheet 33. In FIG. 15, stampers 34 and 35 havinguneven surface prepared by electroforming working from original plateswere mounted in mold cavities 36 and 37. Details of stampers 34 and 35are seen in FIG. 16, wherein 41 is the base of the stamper and 40 is thestamping section of the stamper. The two sheets of superposed laminatedsheets 33 were pressed under heating by the above press portions totransfer unevenness for signal onto both polymethyl methacrylate layers32, followed by cooling and solidification, and two sheets of discequipped with unevenness for signal were punched out at the punchingsection 38 and 39 at the same time. The sheets after punching out werewound up.

What is claimed is:
 1. A method for preparing an optical memory mediumwhich comprises the steps of:laminating a readily deformable resin layercomprising a thermoplastic resin on a heat-resistant sheet comprising athermosetting resin, forming uneven guide grooves on said readilydeformable resin layer, and laminating an optical recording layer on thesurface of the readily deformable resin layer on which said uneven guidegrooves have been formed.
 2. A method for preparing an optical memorymedium according to claim 1, wherein the step of forming an uneven guidegroove on the readily deformable resin layer comprises spreading theresin in a plastic state over the heat-resistant sheet and adhering saidresin onto the heat-resistant sheet by solidification whilesimultaneously forming the uneven guide groove in said resin.
 3. Amethod for preparing an optical memory medium according to claim 2,comprising the step of disposing said readily deformable resin on therespective outer surfaces of two heat-resistant sheets superposed oneach other.
 4. A method for preparing an optical memory medium accordingto claim 1, wherein forming the uneven guide groove on the readilydeformable resin layer includes the steps of spreading the resin in aplastic sate over the heat-resistant sheet, adhering the resin onto theheat-resistant sheet by solidification while forming the uneven guidegroove in said resin, forming a substrate then superimposing on oneanother two sheets of the substrate having aid guide grooves on eachother so that the heat-resistant sheet surfaces contact each other andlaminating optical recording layers on the guide grooves.
 5. A methodfor preparing an optical memory medium according to claim 4, includingthe step of flaminating the optical recording layers by dip coating. 6.A method for preparing an optical memory medium according to claim 2,including the step of spreading the resin by compression molding.
 7. Amethod for preparing an optical memory medium according to claim 2,including the step of spreading the resin by cast molding.
 8. A methodfor preparing an optical memory medium according to claim 2, includingthe step of spreading the resin
 9. A method for preparing an opticalmemory medium according to claim 1, wherein said readily deformableresin layer comprises a thermoplastic resin.
 10. A method for preparingan optical memory medium according to claim 1, comprising the step offorming an uneven guide groove on the readily deformable resin layer bylaminating a resin having a heat deformation temperature lower than theheat-resistant sheet and forming the uneven guide groove onto thesurface of said resin layer by pressurizing the resultant laminatedsheet sandwiched between mold cavities having unevenness on the surfaceunder heating.
 11. A method for preparing an optical memory mediumaccording to claim 10, comprising the step of disposing said readilydeformable resin on the respective outer surfaces of the heat-resistantsheets comprising two sheets superposed on each other.
 12. A method forpreparing an optical memory medium according to claim 1, wherein thestep of forming the uneven guide groove on the plastic resin includesthe step of laminating a resin having a heat deformation temperaturelower than the heat deformation temperature of the heat-resistant sheetand transferring the uneven guide groove onto the surface of said resinlayer by pressurizing and heating the resultant laminated sheetsandwiched between mold cavities having unevenness on the surface,forming a substrate, then superimposing on one another two sheets of thesubstrate having guide grooves so that the surfaces of theheat-resistant sheets contact each other and laminating opticalrecording layers on both external surfaces having the guide grooves. 13.A method for preparing an optical memory medium according to claim 12,including the step of duplicating the optical recording layers.
 14. Themethod for preparing an optical memory medium according to claim 1,wherein an adhesion layer is sandwiched between said thermoplastic resinlayer and said heat-resistant sheet.
 15. A method for preparing anoptical memory medium according to claim 1, wherein the heat-resistantsheet of said optical memory medium has a thickness smaller than that ofthe readily deformable resin layer.
 16. A method for preparing a thintype disc which comprises the steps of:spreading a thermoplastic resinin a plastic state over the respective outer surfaces of twoheat-resistant sheets at least one of said sheets comprising athermosetting resin, one hat-resistant sheet being superposed on theother heat resistant sheet, to form thermoplastic resin layers; andadhering the thermoplastic resin layers with solidification onto theheat-resistant sheets while forming an unevenness for signal onto saidthermoplastic resin layers.
 17. A method for preparing a thin type discaccording to claim 16, wherein the spreading of the resin in the plasticstate onto said two sheets of heat-resistant sheets is performedsimultaneously.
 18. A method for preparing a thin type disc according toclaim 16, including spreading of the resin in a plastic state bycompression molding.
 19. A method for preparing a thin type discaccording to claim 16, including spreading the resin in a plastic stateby cast molding.
 20. A method for preparing a thin type disc accordingto claim 16, including spreading the resin in a plastic state byinjection molding.
 21. A method for preparing a thin type disc accordingto claim 16, wherein aid heat-resistant sheets each comprise athermosetting resin.
 22. The method for preparing an optical memorymedium according to claim 16, wherein an adhesion layer is sandwichedbetween each said resin layer and each said heat-resistant sheet.
 23. Amethod for preparing a thin type disc which comprises (a) laminatingover the respective outer surfaces of two heat-resistant sheets a resinhaving a lower heat deformation temperature than said heat-resistantsheets to form a resin layer laminated to each said heat-resistantsheet, (b) superposing both of said laminated sheets on one another sothat the heat-resistant sheet surfaces contact each other, (c) formingan unevenness for embodying a signal onto each said resin layer surfaceby pressurizing and heating the superposed laminated sheets sandwichedbetween opposed mold cavities, each opposed mold cavity having an unevensurface and thereafter cooling and solidifying the resin layers.
 24. Amethod for preparing a thin type disc according to claim 23, includingthe step of forming the unevenness for embodying a signal in the resinlayer surface of the laminated sheets at the same time.
 25. A method forpreparing a thin type disc according to claim 23, wherein the resinlayer comprises a thermoplastic resin.
 26. A method for preparing a thintype disc according to claim 23, wherein the heat-resistant sheetcomprises a thermosetting resin.
 27. The method for preparing an opticalmemory medium according to claim 23, wherein an adhesion layer issandwiched between each said resin layer and each said heat-resistantsheet.
 28. A method for preparing optical memory sheets comprising thesteps of:laminating two heat-resistant sheets, forming readilydeformable resin layers on both surfaces of the laminated heat-resistantsheets, said resin layers comprising a resin having a lower thermaldeformation temperature than the two heat-resistant sheets; pressing thelaminated heat-resistant resin sheets bearing readily deformable resinlayers using a metal mold having unevenness on its surface to transferuneven guide grooves onto each of the readily deformable resin layers;forming recording layers on the surfaces of the readily deformable resinlayers having the uneven guide grooves, and separating the laminatedheat-resistant sheets from each other.